Preparation and Reactivity of the Versatile Uranium(IV) Imido Complexes U(NAr)Cl₂(R₂bpy)₂ (R = Me, ^tBu) and U(NAr)Cl₂(tppo)₃

Abstract

Uranium tetrachloride undergoes facile reactions with 4,4'-dialkyl-2,2'-bipyridine, resulting in the generation of UCl4(R2bpy)2, R = Me, (t)Bu. These precursors, as well as the known UCl4(tppo)2 (tppo = triphenylphosphine oxide), react with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide the versatile uranium(IV) imido complexes, U(NDipp)Cl2(L)n (L = R2bpy, n = 2; L = tppo, n = 3). Interestingly, U(NDipp)Cl2(R2bpy)2 can be used to generate the uranium(V) and uranium(VI) bisimido compounds, U(NDipp)2X(R2bpy)2, X = Cl, Br, I, and U(NDipp)2I2((t)Bu2bpy), which establishes these uranium(IV) precursors as potential intermediates in the syntheses of high-valent bis(imido) complexes from UCl4. The monoimido species also react with 4-methylmorpholine-N-oxide to yield uranium(VI) oxo-imido products, U(NDipp)(O)Cl2(L)n (L = (t)Bu2bpy, n = 1; L = tppo, n = 2). The aforementioned molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent sources of U(IV), U(V), and U(VI) imido species.

Synthesis and Reduction of Uranium(V) Imido Complexes with Redox‐Active Substituents

“…In the case of the Meyer uranium (IV) tritylimido compound, the U=N‐C bond angle was more compressed (153.3(2)°) than those of the compounds that we have reported in the bis(trimethylsilyl)amide ligand framework, which range from 165.8(5)° for compound 4‐K to 169.82(12)° for K[U IV (=NCPh 3 ][N(SiMe 3 ) 2 ] 3 . Uranium(IV) imido compounds that do not have close interactions with potassium ions, such as U IV (=NDipp)Cl 2 (tppo) 3 reported by Boncella and co‐workers, have similar U=N bond lengths (1.995(5) Å) but more linear U=N‐C bond angles (177.7(4)°) …”

“…The U=Nb ond lengths in compounds 3-K and 4-K (2.001(9) and 2.032(3) )c ompared wellw ith the uranium(IV) tritylimido compounds reported by the Meyer group [36] and our group, [37] K[(( nP,Me ArO) 3 3 .U ranium(IV) imido compounds that do not have close interactions with potassium ions, such as U IV (=NDipp)Cl 2 (tppo) 3 reportedb yB oncella and co-workers, have similar U=Nb ond lengths (1.995(5) )b ut more linear U = N-C bond angles (177.7(4)8). [69] When compounds 2 and 3 were reactedw ith an excess of potassium graphite, the reaction mixtures became dark blue. 1 HNMR revealed many peaks between 8.04-6.88 ppm, al arge amount of HN(SiMe 3 ) 2 ,a nd numerous paramagnetically shifted peaks between À1.66 and À28.87 ppm.…”

Oxo Ligand Substitution in a Cationic Uranyl Complex: Synergistic Interaction of an Electrophile and a Reductant

“…U-O = 2.31 Å) is slightly shorter than the average U-O dppmo distance in the uranyl starting material, [U VI O 2 (dppmo) 2 18 but is similar to other U(IV) phosphine oxide complexes. [24][25][26] Figure S3). The broadness of these resonances is suggestive of exchange of the inner-and outer-sphere triflate moieties at a rate that is comparable to the NMR time scale.…”

CO2 conversion to phenyl isocyanates by uranium(vi) bis(imido) complexes

“…Like complexes 2 and 3, 4 exhibits an octahedral geometry about the uranium center, with the {( Crystallographically characterized trans-[OQUQNR] 2+ compounds are scarce, mostly prepared by oxygen atom transfer to U(IV) monoimido complexes or reductive cleavage of nitrite by a U(V) imido complex. [30][31][32] 33 We have shown here the first activation of CO 2 by a U(VI) imido complex, specifically a trans-bis(imido), with formation Scheme 1 Synthesis of uranium(VI) bis(imido) complexes 2 and 3.…”